Drum type washing machine

ABSTRACT

A drum type washing machine of the present invention is a direct-drive washing machine including a washing-machine casing; a rotating drum with its drum rotation shaft horizontal or inclined; and a motor driving the rotating drum. The motor has a stator including a coil wound in a toroidal winding form and first molding resin; and a twin-type rotor including an outer rotor, an inner rotor, and second molding resin integrally molding them.

TECHNICAL FIELD

The present invention relates to a direct-drive drum type washing machine including a rotating drum with its rotation central axis horizontal or inclined, and a motor driving the rotating drum.

BACKGROUND ART

For fully automatic washing machines of recent years, direct-drive drum type washing machines with a drying function added have been mainstream. A motor for driving a rotating drum of such a washing machine, directly driving the rotating drum not through a gear, needs to implement simultaneously low speed and high torque (from 10 rpm to 100 rpm, 10 N·m or higher) for washing; and high speed and low torque (1,000 rpm or higher) for dewatering. While washing, at an extremely low speed, cogging torque (largely influencing vibration and noise of the washing machine) of the motor needs to be reduced.

As a technique implementing such a motor producing low speed and high torque, a washing-machine motor is known as described in patent literatures 1 and 2. A washing-machine motor described in the patent literatures includes a stator, and a rotor arranged in the outer circumference of the stator. However, as described in patent literature 1, for a motor with a single stator and a single rotor to produce high torque, the amount of the coil wound around the stator, and/or the magnetic force of the rotor need to be increased. Accordingly, the overall volume of the machine body undesirably increases. Further, a washing-machine motor described in patent literature 1 includes a coil wound around the stator by concentrated winding method. Hence, this type of motor generates a radial force higher than that including a coil wound by distributed winding method. Herewith, noise and vibration while driving undesirably increase.

Under the circumstances, to eliminate the above-described problems, a motor as described in patent literature 2 is devised. A motor described in patent literature 2 includes a hollow cylinder-shaped stator having a coil produced by winding a wire around teeth by concentrated winding method; an inner rotor arranged leaving an even gap off the inner circumferential surface of the stator; an outer rotor arranged leaving an even gap off the outer circumferential surface of the stator. A motor with such a structure described in patent literature 2 can use a force caused by magnetic flux of the inner rotor and that of the outer rotor. Accordingly, the motor can increase power density and produce high torque in spite of its small size.

However, a motor described in patent literature 2 as well, including a coil wound by concentrated winding method, generates a high radial force. Herewith, vibration and noise undesirably increase.

Hence, with a drum type washing machine including a washing-machine motor as described in patent literatures 1 and 2, it is undesirably difficult to simultaneously implement higher capacitance, compactification, and noise reduction.

[Patent literature 1] Japanese Patent Unexamined Publication No. 2007-089282

[Patent literature 2] Japanese Translation of PCT Publication No. 2005-521378

SUMMARY OF THE INVENTION

A drum type washing machine of the present invention includes a washing-machine casing having an opening through which laundry is loaded and unloaded; a rotating drum having its drum rotation shaft in a horizontal or inclined direction relative to the casing; and a motor driving the rotating drum. The washing machine is a direct-drive one in which the drum rotation shaft is directly connected to the motor shaft.

The stator of the motor includes a ring-like stator yoke; plural outer teeth projecting from the stator yoke in the outer circumferential direction; plural (the equal number as outer teeth) inner teeth projecting from the stator yoke in the inner circumferential direction; plural outer slots formed between each outer teeth; and plural inner slots placed between each inner teeth. The stator further includes a coil connected to the stator yoke between the outer slot and the inner slot in a shape of three-phase star or delta, wound in a toroidal winding form; and first molding resin integrally molding the stator yoke, outer slot, inner slot, and coil.

Further, the rotor of the motor is twin-type and includes an outer rotor disposed facing the outer teeth through a given air gap; an inner rotor disposed facing the inner teeth through a given air gap; second molding resin integrally molding the outer rotor and the inner rotor; and a motor shaft connected to the outer rotor and the inner rotor.

With a drum type washing machine of the present invention according to the structure, the capacity of laundry can be increased to a maximum extent in spite of its small size, and vibration and noise are reduced to implement low noise allowing night-time operation. Additionally, the invention improves resistance to water and drip to implement a highly reliable washing machine.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a drum type washing machine according to an embodiment of the present invention.

FIG. 2 is a perspective view of motor 5 of the drum type washing machine according to the embodiment of the present invention.

FIG. 3 is an explanatory perspective view showing the stator and the rotor of motor 5 of the same, disassembled.

FIG. 4 is an explanatory perspective view of the same, viewed from a different direction.

FIG. 5 is a sectional view of motor 5 of the same.

FIG. 6 is a sectional view showing a cross section in FIG. 5, taken along line 6-6.

FIG. 7 is a graph showing relationship between the width of a teeth tip and cogging torque in motor 5 of the same.

FIG. 8 is a graph showing relationship between a rotational position (electrical angle) and induced voltage of the rotor of motor 5 of the same.

FIG. 9 is a graph showing relationship between a rotational position (electrical angle) and a radial force of the rotor of motor 5 of the same.

FIG. 10 is a graph showing relationship between a rotational position (electrical angle) and cogging torque of the rotor of motor 5 of the same.

FIG. 11 is a graph showing power density of motor 5 of the same, for each type of motor.

FIG. 12 is a graph showing relationship between the number of poles and a torque constant of motor 5 of the same.

FIG. 13 schematically shows circumstances of currents flowing through coil 15 of motor 5 of the same.

REFERENCE MARKS IN THE DRAWINGS

-   -   1 Washing-machine casing     -   1 a Opening     -   2 Rotating drum     -   3 Water receiving tub     -   4 Drum rotation shaft     -   5 Motor     -   9 Lid     -   10 Stator     -   11 Stator core     -   12 Outer teeth     -   13 Inner teeth     -   14 Stator yoke     -   15 Coil     -   16 Outer slot     -   17 Inner slot     -   18 Through hole     -   20 Inner rotor     -   21 Inner rotor yoke     -   22 Inner permanent magnet     -   30 Outer rotor     -   31 Outer rotor yoke     -   32 Outer permanent magnet     -   41 First surface     -   42 Second surface     -   51 First molding resin     -   52 Second molding resin     -   60 Attaching portion     -   61 Motor shaft     -   62 Rib     -   64 Ventilating hole     -   65 Projection     -   71 Straight line connecting the center in the rotation direction         of the outer teeth to the center in the rotation direction of         the inner teeth     -   72 Center arc of stator yoke

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, a description is made of an embodiment of the present invention in reference to some drawings. FIG. 1 is a sectional view of a drum type washing machine according to the embodiment of the present invention.

Washing-machine casing 1 of the drum type washing machine has bottomed, cylindrical water receiving tub 3 arranged therein in a state inclined downward from the front side of body 1 toward the back side. The inside of this water receiving tub 3 rotatably supports bottomed, cylindrical rotating drum 2 so that its drum rotation shaft 4 is inclined downward from the front side of washing-machine casing 1 toward the back side.

The front side of washing-machine casing 1 has opening 1 a formed therein for loading and unloading laundry. Then, opening 1 a is provided with lid 9 made of material such as glass for opening and closing opening 1 a.

The outside of the bottom of water receiving tub 3 has motor shaft 61 of motor 5 directly connected thereto on the same axis as drum rotation shaft 4 of rotating drum 2. Motor 5 can control rotation speed and a rotation direction of rotating drum 2. Motor 5 is fixed to water receiving tub 3 at attaching portion 60 (to be described later) formed on the outer circumference of motor 5 with attaching means such as screws (not shown).

FIG. 2 is a perspective view of motor 5 of a drum type washing machine according to the embodiment of the present invention. FIGS. 3 and 4 are explanatory perspective views of stator 10 of motor 5, and a twin-type rotor including inner rotor 20 and outer rotor 30, disassembled. FIGS. 3 and 4 are perspective views viewed from different directions.

Motor 5 is composed of stator 10, inner rotor 20 facing the internal diameter side of stator 10; and outer rotor 30 facing the external diameter side.

Stator 10 is covered with first molding resin 51 over the substantially whole surface. Inner rotor 20 and outer rotor 30 are integrally molded with second molding resin 52. The outer circumference of stator 10 has five attaching portions 60 arranged thereon at uniform intervals in the rotation direction. These first molding resin 51 of stator 10 and second molding resin 52 of the rotor are integrally molded by being inserted into a resin-molding mold, respectively.

Second molding resin 52 of the rotor has plural ventilating holes 64 penetrating in the direction of motor shaft 61. Second molding resin 52 is provided thereon with plural projections 65 at the part facing stator 10 in the direction of motor shaft 61. Consequently, while inner rotor 20 and outer rotor 30 are rotating, heat generated from stator 10 is agitated. Then, hot airflow occurs in the rotation direction between stator 10, inner rotor 20, and outer rotor 30. This hot airflow flows out through ventilating hole 64 to discharge heat inside motor 5. Further, the back side of second molding resin 52 is provided thereon with plural ribs 62. Accordingly, required strength can be secured while reducing the amount of molding resin.

FIG. 5 is a sectional view of motor 5, and FIG. 6 is a sectional view showing a cross section in FIG. 5, taken along line 6-6. Stator core 11 composing stator 10 includes substantially ring-like stator yoke 14; outer teeth 12 projecting from stator yoke 14 in the outer circumferential direction; and inner teeth 13 (the equal number as outer teeth 12) projecting from stator yoke 14 in the inner circumferential direction. Stator core 11 further has outer slot 16 formed between each outer teeth 12; and inner slot 17 formed between each inner teeth 13. Then, stator 10 further has plural coils 15 wire-connected in a shape of three-phase star or delta by toroidal winding method wound around stator yoke 14 placed between outer slot 16 and inner slot 17, by concentrated winding method.

Here, with motor 5 according to this embodiment, both inner rotor 20 and outer rotor 30 have 20 poles and 12 slots, respectively. The combination of 20 poles and 12 slots brings about the same effect as that by distributed winding in coil arrangement as later described in detail (refer to FIG. 8).

As described above, stator 10 is integrally molded with first molding resin 51 after coil 15 is wound. The purpose is to fix coil 15 to stator core 11 and to prevent moisture and drips. Motor 5 is used for a washing machine, and thus improving moisture-proof and drip-proof properties is particularly important. In addition, when integrally molding with first molding resin 51 in this way, the effect is expected in that molding resin 51 absorbs vibration to reduce vibration and noise of the entire washing machine.

Stator yoke 14 of stator core 11 has plural through holes 18 formed therein penetrating axiswise. When coil 15 is integrally molded with first molding resin 51, molding resin 51 is filled into outer slot 16, inner slot 17, first surface 41 (upper side in FIG. 6) of stator yoke 14, second surface 42 (lower side in FIG. 6) of stator yoke 14, and through holes 18. With such a structure, first molding resin 51 on first surface 41 of stator yoke 14 is to be connected to first molding resin 51 on second surface 42 through first molding resin 51 filled into through holes 18. Hence, even if first molding resin 51 on first surface 41 and first molding resin 51 on second surface 42 are formed thinly to downsize the motor, exfoliation is prevented owing to molding resin 51 filled into through holes 18 being connected. Here, attaching portions 60 are formed on second surface 42 from first molding resin 51.

Each of through holes 18 is provided at the intersecting point of straight line 71 connecting the rotation-direction centers of outer teeth 12 and inner teeth 13, passing through the rotation-direction centers; and center arc 72 of stator yoke 14. The shape of a cross section of through hole 18 is preferably circular or elliptical, which is because the fluidity of the molding resin material is increased.

The radial length of through hole 18 is preferably 0.5±10% that of stator yoke 14. This is because a longer one causes magnetic saturation in stator yoke 14 to decrease the motor torque; a shorter one causes lower fluidity of the molding resin when molding to decrease the strength. Here, the shape of a cross section of through hole 18 is not limited to circular or elliptical, but quadrangle, rectangle, triangle, or the like may be used as appropriate.

First molding resin 51 and second molding resin 52 are ideally unsaturated polyester resin containing a filler, which is because the resin is excellent in fluidity during molding and in strength after molding.

FIG. 7 is a graph showing relationship between the width of a teeth tip and cogging torque. The broken line in the figure represents relationship between the width of a tip of inner teeth 13 and cogging torque, where only inner rotor 20 is assumed to be present. The solid line represents relationship between the width of a tip of outer teeth 12 and cogging torque, where only outer rotor 30 is assumed to be present.

FIG. 7 proves that to minimize the cogging torque, the width of a teeth tip needs to be increased. In FIG. 7, the cogging torque becomes lower particularly near 14.5 degrees and 19.3 degrees. In such a case, the length (the pitch of teeth at their part with the maximum width) of a slot open becomes shorter, and thus the amount of first molding resin 51 filled into a slot open decreases. In this embodiment, however, first molding resin 51 filled into plural through holes 18 penetrating axiswise of stator yoke 14 connects first molding resin 51 on first surface 41 to first molding resin 51 on second surface 42. Herewith, even if the amount of first molding resin 51 filled into a slot open decreases, a strong fixing strength of first molding resin 51 on stator core 11 is implemented.

Outer rotor 30 is disposed facing outer teeth 12 through a given air gap. Similarly, inner rotor 20 is disposed facing inner teeth 13 through a given air gap.

Outer rotor 30 includes outer rotor yoke 31, and plural outer permanent magnets 32 embedded into outer rotor yoke 31. Outer rotor yoke 31 has magnetic steel sheets laminated thereon punched into a given shape to form a magnetic circuit.

Similarly, inner rotor 20 includes inner rotor yoke 21, and plural inner permanent magnets 22 embedded into inner rotor yoke 21. Inner rotor yoke 21 has magnetic steel sheets laminated thereon punched into a given shape to form a magnetic circuit. Here, outer rotor 30 and inner rotor 20 do not include a rotor frame, respectively. Accordingly, the weight and manufacturing worker-hours can be reduced. Further, the amount equivalent to the volume of a frame can be covered with second molding resin 52, thereby absorbing vibration.

The description is made of the case where outer permanent magnet 32 and inner permanent magnet 22 are embedded into their respective rotor yokes (what is called magnet-embedded type), but either one of them may be disposed on the surface of the rotor yoke (what is called surface-magnet type). However, either one of them needs to be of magnet-embedded type in order to implement high torque and high power with the aid of reluctance torque.

As described above, outer rotor 30 and inner rotor 20 are inserted into a resin-molding mold to be integrally molded with second molding resin 52. Then, they are integrally connected to motor shaft 61. Energizing coil 15 with a given current rotates outer rotor 30 and inner rotor 20 integrally. With outer rotor 30 and inner rotor 20 thus structured integrally, motor 5 provides higher torque and higher power than typical inner- and outer-rotor motors.

FIG. 8 is a graph showing relationship between a rotational position (electrical angle) and induced voltage of the rotor. FIG. 8 shows experimental results for rotors where relationship between the number of slots S and the number of poles P holds S:P=3:2N−1 (excluding a case where 2N−1 is a multiple of 3).

FIG. 8 proves that if S:P=3:2N−1 (excluding a case where 2N−1 is a multiple of 3) holds, a substantially sine wave is produced same as that with a coil by distributed winding method. Further, the waveform of the induced voltage is a sine wave, thereby restraining noise and vibration of motor 5 in the same way as by distributed winding method.

Here, a description is made of the reason why a substantially sine wave is produced same as that with a coil by distributed winding method when S:P=3:2N−1 (excluding a case where 2N−1 is a multiple of 3) holds.

FIG. 13 schematically shows circumstances of a current flowing through coil 15. Coil 15 is wound sequentially in the order of U phase, V phase, and W phase. Reverse currents flow through coils 15 wound around adjacent slots. That is to say, when a current is flowing through a U-phase coil 15 from inner slot 17 to outer slot 16, another current flows through adjacent V-phase coil 15 from outer slot 16 to inner slot 17. Yet another current flows through W-phase coil 15 adjacent to V-phase coil 15 from inner slot 17 to outer slot 16.

With such a structure, reverse currents are to flow through U-phase coil 15 and next U-phase coil 15, which thus the currents shown by broken lines are to flow in a pseudo manner. The currents shown by the broken lines are the same as those with a distributed coil. Accordingly, when S:P=3:2N−1 (excluding a case where 2N−1 is a multiple of 3) holds, the currents flow in the same way as those by distributed winding method, which produces a substantially sine wave same as that by distributed winding method.

FIG. 9 shows relationship between a rotational position (electrical angle) and radial force of the rotor. The solid line in FIG. 9 represents a motor (twin-rotor motor by toroidal winding method) according to this embodiment; the broken line represents a single-rotor motor by distributed winding method.

FIG. 9 proves that the twin-rotor motor by toroidal winding method provides a radial force lower than the distributed-winding, single-rotor motor. This is assumed to be because mutually canceling out vibration of the inner rotor and that of the outer rotor can reduce the radial force.

Such effect of radial force reduction is exerted particularly in a direct-drive washing machine rotating at a low speed (10 to 100 rpm) for washing. This is because cogging is likely to influence noise and vibration of the washing machine due to slow rotation.

FIG. 10 shows relationship between a rotational position (electrical angle) and cogging torque of the rotor of a twin-rotor motor by toroidal winding method. In the figure, the thin broken line represents cogging torque by inner rotor 20; the thin solid line, by outer rotor 30; and the central bold solid line, cogging torque of entire motor 5 produced by combining the above torques.

With motor 5 according to the embodiment, inner rotor 20 and outer rotor 30 are structured so that the phase of cogging torque by inner rotor 20 is inverted from that by outer rotor 30. The peak value of cogging torque by inner rotor 20 is made roughly equal to that by outer rotor 30. With such a structure, cogging torque of entire motor 5 can be significantly reduced by mutually canceling out cogging torque by inner rotor 20 and that by outer rotor 30, as shown in FIG. 10.

FIG. 11 shows power density of a motor by each type. Here, power density refers to power per volume of a motor. In FIG. 11, A represents an inner single-rotor motor; B, outer single-rotor motor; C, concentrated-winding twin-rotor motor; and D, toroidal-winding twin-rotor motor according to the embodiment. A hollow part shows the density of power by the inner rotor; a hatched part, by the outer rotor.

FIG. 11 shows that power density of D is the highest. As compared D to A, D has an inner slot area smaller than A, and thus the power density of the inner rotor decreases. D, however, has an outer rotor, and thus exceeds A in overall power density. FIG. 11 shows that D has a power density 1.9 times that of A.

As compared D to B, D has an outer slot area smaller than B, and thus the power density of the outer rotor decreases. D, however, has an inner rotor, and thus exceeds B in overall power density. FIG. 11 shows that D has a power density 1.5 times that of B.

These circumstances show that a washing machine with motor D has a laundry capacity 1.9 times that with motor A; a washing machine with motor D has a laundry capacity 1.5 times that with motor B. In other words, if D, A, and B have an equal power, D can be downsized by 50% by volume compared to A; 35%, to B.

As compared D to C, magnetic flux content passing through rotor yoke D exceeds that through rotor yoke C, when the volumes of both yokes are equal. Accordingly, the overall power density of D exceeds that of C. FIG. 11 shows that D has a power density 1.4 times that of C.

FIG. 12 shows relationship between the number of poles and a torque constant. In FIG. 12, the bold solid line shows experimental results of a motor with S:P=3:2N−1 (excluding a case where N is a multiple of 3). The thin broken line shows experimental results of a motor with S:P=3:2N (conventional, typical case). The thin solid line shows experimental results of a motor with other than the above. FIG. 12 proves that a motor with S:P=3:2N−1 has an excellent torque constant particularly for more than 20 poles. Specifically, what is ideal is the combination of the number of slots S=12 and the number of poles P=20 (i.e. S:P=3:5) described in the embodiment.

The motor described hereinbefore includes a stator having a coil wound in a toroidal winding form; and a twin-type rotor with an outer rotor and an inner rotor, and thus can produce high torque in spite of its small size as well as reducing noise and vibration while driving. The motor includes first molding resin integrally molding the stator yoke, outer slot, inner slot, and coil; and second molding resin integrally molding the outer rotor and inner rotor, thereby reducing the weight and manufacturing worker-hours as compared to a case where molding is performed by using a frame. Further, the amount equivalent to the volume of a frame can be covered with molding resin, thereby absorbing vibration.

Moreover, the stator yoke has plural through holes formed penetrating through both end surfaces thereof, and the molding resin for a stator integrally molds the stator yoke, outer slot, inner slot, coil, and through holes, thereby connecting molding resin on both end surfaces of the stator yoke with molding resin filled in the through holes, which prevents the molding resin covering the stator from exfoliating off the stator.

Further, with the number of slots S and the number of poles P holding S:P=3:2N−1, the waveform of the induced voltage is a sine wave, thereby restraining noise and vibration of the motor.

With a drum type washing machine including the motor, the capacity of laundry can be increased to a maximum extent in spite of its small size, and vibration and noise are reduced to implement low noise allowing night-time operation. Additionally, as the invention has the structure covering main portions of motor with molding resin, the invention improves resistance to water and drip to implement a highly reliable washing machine.

INDUSTRIAL APPLICABILITY

A drum type washing machine according to the present invention is useful as a washing machine producing high torque in spite of its small size, and reducing noise and vibration while driving. 

1. A drum type washing machine comprising: a washing-machine casing having an opening through which laundry is loaded and unloaded; a rotating drum having a drum rotation shaft in a horizontal or inclined direction relative to the casing; and a motor driving the rotating drum, wherein the machine is a direct-drive washing machine the drum rotation shaft of which is connected directly to a motor shaft of the motor, and wherein the motor includes: a stator having: a ring-like stator yoke; a plurality of outer teeth projecting from the stator yoke in an outer circumferential direction; a plurality, the equal number as the outer teeth, of inner teeth projecting from the stator yoke in an inner circumferential direction; a plurality of outer slots formed between each of the outer teeth; a plurality of inner slots formed between each of the inner teeth; a coil wire-connected to the stator yoke between the outer slot and the inner slot in a shape of a three-phase star or a delta, wound in a toroidal winding form; and first molding resin integrally molding the stator yoke, the outer slot, the inner slot, and the coil; and a twin-type rotor having: an outer rotor disposed facing the outer teeth through a given air gap; an inner rotor disposed facing the inner teeth through a given air gap; second molding resin integrally molding the outer rotor and the inner rotor; and the motor shaft connected to the outer rotor and the inner rotor.
 2. The drum type washing machine of claim 1, wherein the rotating drum has a bottomed, cylindrical water receiving tub at an outer circumference thereof, and the motor is fixed to a bottom of the water receiving tub.
 3. The drum type washing machine of claim 2, wherein the first molding resin has a plurality of attaching portions, which are fixed to the water receiving tub.
 4. The drum type washing machine of claim 1, wherein the stator yoke has a plurality of through holes penetrating axiswise, and wherein the first molding resin integrally molds the stator yoke, the outer slot, the inner slot, the coil, and the through holes.
 5. The drum type washing machine of claim 4, wherein each of the through holes is formed at an intersecting point of a straight line connecting a rotation-direction center of the outer teeth to a rotation-direction center of the inner teeth; and a center arc of the stator yoke.
 6. The drum type washing machine of claim 4, wherein the through holes have circular or elliptical cross sections.
 7. The drum type washing machine of claim 1, wherein the second molding resin has a plurality of ventilating holes penetrating in a direction of the motor shaft.
 8. The drum type washing machine of claim 1, wherein the second molding resin has a plurality of projections at a part thereof facing the stator in a direction of the motor shaft.
 9. The drum type washing machine of claim 1, wherein the second molding resin has a plurality of ribs at a back side thereof.
 10. The drum type washing machine of claim 1, wherein the number (S) of the outer slots is equal to that of the inner slots, wherein the outer rotor includes an outer rotor yoke and an outer permanent magnet with the number of poles P, wherein the inner rotor includes an inner rotor yoke and an inner permanent magnet with the number of poles P, and wherein the number of slots S and the number of poles P hold S:P=3:2N−1, where integer N is 1 or more, and a case where 2N−1 is a multiple of 3 is excluded.
 11. The drum type washing machine of claim 10, wherein the number of slots S and the number of poles P hold S:P=3:5.
 12. The drum type washing machine of claim 10, wherein at least one of the outer permanent magnet and the inner permanent magnet is embedded into an inside of the outer rotor yoke or the inner rotor yoke. 